This invention relates generally to motion picture photography and, more particularly, to an improved mounting arrangement for an idler roller in a multipurpose sound motion picture film handling cassette against which a constant speed drive capstan biases said film strip.
The present invention is directed to a roller mounting arrangement particularly useful in connection with photographic film cassettes from which the film strip need not be removed during the exposure, processing and projection operations and, more particularly, to film cassettes of the type which include internally programmed film processing systems. Exemplary of such systems are those described in the commonly assigned U.S. Pat. No. 3,785,727 of John F. Batter Jr., et al. As described in the above-referenced patent, a motion picture system has been devised by which a supply of photographic film contained in a cassette can be exposed in a camera adapted to receive the cassette and then processed, or developed, to provide the conventional series of transparent image frames in accordance with the transport of the film strip in a predetermined program.
It has also been proposed that the film strip, in addition to carrying a photosensitive area, carry a magnetic sound track affixed to or formed as a part thereof. Such film strip and magnetic track combinations have been marketed for motion picture cameras and projectors and are commonly used within the photographic art. Whether such films have the magnetic track affixed to it or formed as a part of it, recording may be carried out in either the camera or, subsequent to exposure, in a projector type arrangement in which "fill-in" or background comments are provided. When sound recording and playback occurs, both a magnetic transducer head and a constant speed drive capstan must be introduced through the cassette structure in order to contact the magnetic track portion of the film strip. A constant speed drive capstan is employed for moving the film strip and magnetic track past the transducer head at a constant speed in order to achieve a good quality of sound recording. In contradistinction to the constant speed drive of the capstan, is the incremental motion imparted to the film strip by the sprocket drive mechanism of the camera and the projector. Such mechanisms generally take the form of a claw which pulls the film by engaging sprocket holes on one or both sides of the film strip. As previously suggested, such mechanisms move the film strip along the given path of travel in a motion which is not unlike a flutter or twitch. Typically, the constant speed drive and the incremental advancement drive are isolated by formation of a slack film loop. Such a system for use in a cassette of the type described above, is illustrated and described in U.S. Pat. No. 3,921,880 entitled "Multipurpose Audio-Visual Cassette with Isolation Loop" of Donald T. Scholz.
As illustrated in the above-referenced patent, the constant speed drive system typically comprises a displaceably mounted constant speed drive capstan that selectively engages the film against a film guide roller. In cassettes of this type, the cassette housing is typically made from a molded thermoplastic material. The supporting posts for film guide rollers, film supply reels and various other internal structure of the cassette are typically integrally formed with the cassette housing and accordingly made from the same thermoplastic material.
Unlike conventional film cassettes of the type wherein the film strip is removed from the housing and processed in a laboratory, the guide rollers in a multipurpose film handling cassette of the type described hereinabove must be designed to contact the film strip only at the outer edges thereof to minimize contact with the central emulsion layer of the film strip. Consequently, such guide rollers are formed having a centrally depressed area and two stepped portions proximate the lateral edges of the film strip. Configured as such, the wet emulsion layer of the film strip following deposition of the processing fluid is isolated from contact with the idler rollers by this central depressed area. The outer edges of the film strip which are in contact with the stepped portions are not coated with the developing liquid and such contact does not affect the quality of the film strip or its image. In conventional film cassettes wherein the film strip is removed for processing, the idler roller against which the constant speed drive capstan sandwiches the magnetic track bearing portion of the film is typically provided with a resilient outer covering whereby the film strip may be positively sandwiched between the constant speed drive capstan and the idler roller with full contact of the film strip with both of these elements and in fact actual contact between the drive capstan and the surface of the idler roller. A nominal force imparted by the capstan accordingly results in good driving contact with the film strip.
In order to assure a positive constant speed drive in a multipurpose film cassette of the type described above, the drive capstan has been adapted to urge the film against the idler roller with a force on the order of 700 to 800 grams. Such force would result in the bending of the mounting post for the idler roller which serves to backup the constant speed drive capstan, resulting in undesirable skew driving of the film strip therethrough. Molding of a sufficiently rigid bearing post from the cassette material was not conveniently possible because of space limitations and limitations upon the thickness of parts which can be molded from a thermoplastic material without resulting in undesirable effects during cooling of the material. Furthermore, in order to minimize frictional drag and erratic rotation, a small diameter mounting post is extremely desirable.